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Post Retirement Benefits (Details) - USD ($)
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2010
Amounts that will be amortized from accumulated other comprehensive income in next fiscal year:          
Interest cost   $ 285,000 $ 277,000 $ 298,000  
Postretirement benefits          
Postretirement benefits:          
Decrease in post retirement obligations         $ 10,282,000
Amortization period         20 years
Change in net periodic benefit cost due to plan amendment   496,000 496,000 $ 496,000  
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)   1,099,000 910,000    
Amounts that will be amortized from accumulated other comprehensive income in next fiscal year:          
Interest cost   $ 285,000 $ 277,000    
Assumed health care cost trend rates:          
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year   6.00% 6.20%    
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate   5.00% 5.00%    
Effect of changing the health care cost trend rate by one-percentage point for each future year:          
Effect on total of service and interest cost components, 1 - percentage point increase   $ 39,000      
Effect on total of service and interest cost components, 1 - percentage point decrease   (33,000)      
Effect on post retirement benefit obligation, 1 - percentage point increase   1,169,000      
Effect on post retirement benefit obligation, 1 - percentage point decrease   $ (997,000)      
Scenario, Forecast [Member] | Postretirement benefits          
Postretirement benefits:          
Change in net periodic benefit cost due to plan amendment $ 496,000        
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) (78,000)        
Amounts that will be amortized from accumulated other comprehensive income in next fiscal year:          
Amortization of prior service credit, net of tax (496,000)        
Amortization of loss, net of tax (181,000)        
Interest cost $ 237,000